The genetics of the human mitochondria and their role in neoplastic transformation will be studied using cultured human cells. Two human cancer lines as well as selected normal fibroblasts and their SV40-transformed derivatives have been collected and appropriate nuclear and cytoplasmic markers introduced. These lines, which originated from a variety of different origins, are being screened for mitochondrial DNA (mtDNA)-sequence polymorphisms using restriction endonucleases and heteroduplex analysis and for mitochondrial polypeptide variants using various electrophoresis produces and monoclonal antibodies against the inner membrane proteins. The mtDNA-sequence polymorphisms will then be used to assign selectable and polymorphic markers to the mtDNA and nuclear DNA. MtDNA-coded variants will be used in a detailed molecular analysis of mitochondrial gene segregation, studies on nucleocytoplasmic interaction, and in the development of new mitochondrial gene transfer technologies using purified mitochondria and mtDNA. Finally, the available nuclear and cytoplasmic genetic markers together with new gene transfer and selection procedures will be used to test a genetic hypothesis of neoplastic transformation and to investigate the role of mitochondrial or other cytoplasmic genes in this process.